The invention pertains to a process for the preparation of regenerated cellulose filaments from an anisotropic solution containing cellulose formate, phosphoric acid, and formic acid, which process comprises the following steps:
extruding the solution through capillaries, PA1 passing the formed cellulose formate filament through a layer of air, PA1 passing the cellulose formate filaments through a coagulation bath, PA1 washing the cellulose formate filaments with water, PA1 regenerating the cellulose formate filaments, PA1 washing the formed regenerated cellulose filaments with water, PA1 drying the regenerated cellulose filaments, and PA1 winding the regenerated cellulose filaments. PA1 0&lt;DS&lt;1%, PA1 CV&lt;2, PA1 breaking load: 700-1200 mN/tex, PA1 elongation at break &gt;5%. PA1 0&lt;DS&lt;1%, PA1 CV&lt;2, PA1 breaking load: 700-1200 mN/tex, and PA1 elongation at break &gt;5%. PA1 The filaments do not exhibit a banded structure. The absence of a banded structure is an indication of the filaments' great structural regularity. This is reflected in a greater yarn regularity. PA1 The filaments have a compression strength of greater than 0,25 GPa. a high compression strength is of advantage if the filaments, optionally in a multifilament yarn, are exposed to a compression load. PA1 The yarn has an initial modulus of higher than 15 N/tex. The initial modulus is a measure of the yarn's stiffness. Such stiffness can be an important factor for various applications. PA1 k=constant=0,25 PA1 V.sub.1 =the quantity (in ml) of 0,1 M NaOH solution used for equivalency point 1, PA1 V.sub.2 =the quantity (in ml) of 0,1 M NaOH solution used for equivalency point 2, PA1 t.sub.1 =the strength of the NaOH solution, and PA1 P=the weighed quantity of dried yarn, with the yarn after being rinsed having been dried for some time at 120.degree. C. PA1 P=the weighed quantity of dried yarn, with the yarn, after rinsing and titration, having been dried for some time at 120.degree. C., PA1 V.sub.4 =the quantity (in ml) of 1,0 M HCl solution used for measuring the yarn specimen, PA1 V.sub.3 =the quantity (in ml) of 1,0 M HCl solution used for the blank determination, and PA1 t.sub.2 =the strength of the HCl solution.
Such a process is known from WO 85/05115.
This patent application discloses the dissolution of cellulose in a solvent containing formic acid and phosphoric acid. The resulting anisotropic solution, which contains cellulose formate, is spinnable and can be processed by means of an air gap-wet spinning process. Cellulose formate filaments obtained in this manner can be regenerated using NaOH.
The resulting regenerated cellulose filaments have a high breaking load and a high modulus as compared with the regenerated cellulose filaments which can be made by the viscose process. However, the elongation at break of the filaments which can be made by the process of WO 85/05115 is comparatively low, generally in the range of 3 to 4%. Moreover, the filaments have a morphology which appears to be built up of layers embedded in each other which surround the axis of the filament. This morphology appears to vary pseudoperiodically along the axis of the filament. Such a pseudoperiodical morphology can also be described as a banded structure. This banded structure can be made visible with a polarisation microscope.
WO 94117136 describes a process for spinning filaments from isotropic solutions containing cellulose formate. While the filaments obtained in this manner have an elongation at break of more than 4%, their breaking load is comparatively low.